In spray paint operations, a paint fluid, commonly in the form of a liquid or a relatively fine powder, is mixed with compressed air to atomize the paint particles and transfer the atomized paint particles onto the surface of an item being painted. Frequently, a paint gun is fluidly connected to a paint source and an air source and mixes the two materials proximate a paint location. Alternatively, many paint guns include a paint container that is physically supported by the paint gun. During most painting operations, it is very important to maintain a clean paint supply in order to ensure a quality finish. The paint fluid is frequently formed from a mixture of resins and colored particulates or flakes. The paint fluid is generally delivered to a mixing point through a series of pipes, tubes, or hoses. Preferably, this fluid path is relatively smooth or free of steps of discontinuities where the resin or color particulates may collect and form an undesirable particulate or resin ball. Understandably, any collection of particulates or resin, whether solid or pliable, introduced into the fluid paint flow can detrimentally affect operation of the paint gun or quality of the paint finish.
One commonly used spray paint gun, commonly referred to as a high volume low pressure (HVLP) spray gun, generates high volumes of low-pressure air which transfers the paint particles to the surface of the article being painted with relatively low velocity. The high volume low velocity transfer of paint to the work piece reduces overspray generated during the painting process and thereby improves the paint to part transfer ratio. In such systems, a fluid regulator regulates the flow of fluid between a high-pressure port and a low-pressure port of the paint gun. Understandably, operation of such systems requires the periodic cleaning of the fluid transfer lines. This cleaning process generally includes passing a fluid having a different viscosity than the paint, such as air, a cleaning agent, or solvent through a pump to remove residual paint from the pump and the fluid paths of the spray system. Solvents are also passed through the pump when it is desired to change the color being applied to a part.
The fluid properties of paint being sprayed and the cleaning agent or other fluids passed through the pump are generally not the same. It is readily appreciated that fluid paints, even paints that have been somewhat thinned for spray application, are generally more viscous than air or cleaning agents. Commonly, when the spray system is to be cleaned for non-use or a color change, the supply of paint is replaced with a supply of cleaning agent that is then run through the system in a manner similar to the paint. Passing solvent through a system configured to deliver a spray of atomized paint undesirably alters the operation of the delivery system.
The introduction of another fluid, such as solvent, a source of air, or an air vacuum condition, to the pump substantially increases the pump reciprocation rate if the air flow is provided at a flow rate associated with moving the thicker paint through the pump. Commonly, after the initial introduction of the second fluid to the fluid system, the pump must be maintained at a paint delivery operating pressure. If the pump operating pressure is prematurely reduced, the pump may have occasion to stall thereby delaying the cleaning process. Conversely, if the pump operating pressure is maintained at a paint delivery pressure after the less viscous fluid overtakes the fluid path of the pump, operation of the pump increases to a level that detrimentally affects pump performance and/or longevity.
Accordingly, it would be desirable to provide a pneumatic tool control system that automatically alters a compressed air flow based on real-time operating characteristics of the pneumatic tool.